It is known from U.S. Pat. No. 4,669,650 to forge weld tubular ends in a reducing environment, wherein a flushing gas, for example hydrogen having less than 100 ppm H2O and/or O2 is flushed around the heated tubular ends to inhibit corrosion and to reduce and flush off an oxidized skin. A disadvantage of using hydrogen as flushing gas is that it will react with oxygen in the atmosphere in an explosive fashion so that it cannot be used in hazardous areas such as on an offshore oil and/or gas production platform or on an oil and/or gas well drilling rig. This prior art reference mentions on page 2, lines 65–68 that instead of using a reducing gas an inert gas may be used as flushing gas and discloses that the tubular end may be heated by means of an induction coil or by means of an unspecified method of high frequency heating.
International patent application WO98/33619 discloses a method for joining oilfield tubulars by diffusion bonding, wherein the tubular ends are heated by an induction coil inside a cavity filled with a shield gas. European patent 0396204 discloses a method for friction welding of well tubulars, wherein a ring is rotated at high speed in a cavity filled with shield gas and the tubular ends are pressed against the ring whereupon the ring and tubular end melt together.
U.S. Pat. No. 5,721,413 discloses a method of heating closely spaced portion of two pipes by heating each pipe end by a pair of diametrically opposite contacts, and the contacts of each pair are arranged in a specific crossed configuration relative to the contacts of the other pair to equalize heating of the pipe ends.
It is an object of the present invention to provide a forge welding method, which is able to interconnect tubular ends with a minimum of oxidized metal inclusions also in hazardous areas, such as on an offshore oil and/or gas production platform or on an oil and/or gas well drilling rig, in a safe and efficient manner and such that the tubular ends are heated in a substantially uniform manner such that a high quality forge weld is created even if the tubulars have an irregular shape.